Vehicle speed detection has been generally based on radar gun systems. Radar guns typically use the emission and detection of reflected electromagnetic waves from the object being interrogated. The relative velocity of the object can then be determined by the Doppler Effect on the reflected waves due to the motion of the vehicle. The Doppler Effect shifts the frequency of the radar reflection based on the relative velocity (speed) of the “target”, allowing for the direct and generally accurate measurement of the speed of a moving vehicle.
However, there are some known problems with radar guns. First, for speed to be accurately calculated, the moving object of interest should be the only moving object in the beam path of the radar gun. If this is not the case, it is not possible to determine which object's speed the system is reading. Second, the incident angle of the beam path of the radar gun to the object can also affect the array of the measurement. This includes angles on horizontal and vertical planes. Third and perhaps most importantly, the active electromagnetic emissions required in such systems, even in the case of laser emitting systems, can be detected by commercially available radar detectors procured by motorists purposefully trying to evade speed limit enforcement efforts. Fourth, radar guns generally do not provide multiple lane support. That is a radar gun generally only measures the speed of one vehicle at a time.
Some have suggested use of passive speed detection systems including one or more cameras, thus being without an electromagnetic wave emission source, to determine the speed of a moving vehicle. However, the use of camera images generally requires interpretation of the motion of a 3-dimensional (3D) object through 2-dimensional (2D) images provided by the camera(s). A significant problem with such an approach is that the 3D information of the vehicle is projected or nonlinearly transformed into 2D information. Hence, techniques or methods are needed to obtain 3D information despite the fact that only 2D information is available. Moreover, such systems generally lack multiple lane support.